Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 99,646	$ 51,562
Short-term investments	29,630	39,178
Accounts receivable, net of allowance for doubtful accounts of $1,407 and $1,478 at March 31, 2018 and December 31, 2017, respectively	38,718	73,661
Deferred contract acquisition and fulfillment costs, current portion	8,583	0
Prepaid expenses and other current assets	12,232	8,877
Total current assets	188,809	173,278
Long-term investments	1,096	1,102
Property and equipment, net	9,238	8,589
Goodwill	83,164	83,164
Intangible assets, net	16,316	16,640
Deferred contract acquisition and fulfillment costs, non-current portion	20,295	0
Other assets	1,552	1,363
Total assets	320,470	284,136
Current liabilities:
Accounts payable	5,669	2,240
Accrued expenses	18,372	29,728
Deferred revenue, current portion	140,448	155,811
Other current liabilities	1,702	1,706
Total current liabilities	166,191	189,485
Deferred revenue, non-current portion	78,450	68,689
Other long-term liabilities	1,907	1,809
Total liabilities	246,548	259,983
Stockholders’ equity:
Preferred stock, $0.01 par value per share; 10,000,000 shares authorized at March 31, 2018 and December 31, 2017; 0 shares issued at March 31, 2018 and December 31, 2017	0	0
Common stock, $0.01 par value per share; 100,000,000 shares authorized at March 31, 2018 and December 31, 2017; 46,685,380 and 44,540,544 shares issued at March 31, 2018 and December 31, 2017, respectively; 46,198,572 and 44,053,736 shares outstanding at March 31, 2018 and December 31, 2017, respectively	462	441
Treasury stock, at cost, 486,808 shares at March 31, 2018 and December 31, 2017	(4,764)	(4,764)
Additional paid-in-capital	503,669	463,428
Accumulated other comprehensive loss	(44)	(39)
Accumulated deficit	(425,401)	(434,913)
Total stockholders’ equity	73,922	24,153
Total liabilities and stockholders’ equity	$ 320,470	$ 284,136